POPULAR MISCELLANY. 



713 



and land-slides, which give the place a curi- 

 ous aspect. The mines belong to the Gov- 

 ernment, as do also the salt-mines, and are 

 farmed out for a small sum. They are 

 not very actively worked, and the product 

 is small. The process for extracting the 

 gems is much like that pursued in mining 

 for the sale, except that, instead of using a 

 ball of clay, the miners burn a bunch of dry 

 grass in the hole, taking precaution, as soon 

 as the cracks appear, not to damage the tur- 

 quoises which may be incased in the block. 

 The stones are generally found in groups, 

 often numbering twenty-five or thirty, in- 

 crusted with a thin calcareous envelope 

 which is white next to the mineral, brown 

 on the side next to the rock. The khaki, 

 or earthy turquoises, are found in the valley 

 adjoining the hills, in a soil composed of 

 gravel and rounded stones resting on a clay 

 subsoil. After the earth has passed through 

 two or three washings, a considerable num- 

 ber of turquoises are left, of moderate 

 size, but pale and of little value, if the dig- 

 gings are fresh. The turquoises in the older 

 pits have a better color, because, the miners 

 say, the stones acquire their color with age. 

 Among the largest turquoises which have 

 been mentioned are one of which a drink- 

 ing-cup was made for the Shah of Persia, 

 and one in which the treasure of Venice was 

 kept, and which weighed several pounds. 

 Generally the large turquoises are pale or 

 discolored, and of little value, and are used 

 principally for the decoration of furniture, 

 and of the saddles and bridles of rich Per- 

 sians. 



Heat in Tnunel - Excavations. Dr. F. 



M. Stapff, engineering geologist of the St. 

 Gothard Tunnel, has published, in the " Re- 

 vue Universelle des Mines," the results of 

 the studies he made during the progress of 

 the operations in the tunnel as to the high- 

 est temperature at which men can work un- 

 derground, and the depth below the surface 

 at which that temperature is likely to be met 

 in tunneling. The limit of temperature at 

 which men can work depends upon the 

 length of their exposure, the amount of ex- 

 ertion they put forth, their condition, and 

 the nature of the atmosphere, particularly 

 as to its degree of moisture. It is certain 

 that men can not become used to stand, for 



any length of time, a higher degree of tem- 

 perature than from 140 to 165 Fahr., even 

 when they keep perfectly still, and are in 

 quite pure air. Men have worked at 104 

 on railways in the United States and Mexico, 

 at 72 to 94 in Belgian collieries, at 125, 

 under exceptionally favorable conditions, in 

 the Fahlun copper-mine in Sweden, and are 

 said to work occasionally in the stoke-holes 

 of tropical steamers at 156. The highest 

 temperature observed in the Mont Cenis 

 Tunnel was 86. In the St. Gothard Tunnel 

 work was carried on at 87 on the Airolo 

 side, in an atmosphere saturated with moist- 

 ure, and at 84 on the Goschenen side, in an 

 atmosphere less highly impregnated. Pro- 

 fessor Du Bois-Reymond estimates that men 

 can stand a temperature of 122 when the 

 air is as dry as possible, but that even 104 

 is likely to be fatal in an atmosphere satu- 

 rated with moisture ; and he recommends 

 quick lime, notwithstanding the heat it gives 

 off, as preferable for counteracting the heat, 

 because it absorbs the moisture, to ice, which 

 adds to it. Salt and ice are, however, good. 

 The highest limit of air-temperature theoret- 

 ically possible in tunnel-work would be that 

 which would induce fever-heat, or 107 in 

 tiie body ; the highest practicable, but still 

 a dangerous, temperature should not raise 

 the heat of the body over 104. On this ba- 

 sis an extreme temperature of 114 would be 

 admissible at the Goschenen end, and of 100 

 at the Airolo end, of the St. Gothard Tunnel. 

 The temperature within the borings of the St. 

 Gothard Tunnel was found to increase with 

 the depth of the excavation, at a general av- 

 erage rate of 1 Fahr. per 88"1 feet of verti- 

 cal depth below the surface of the mountain. 

 The rate is subject to local variations, giv- 

 ing sometimes as much as 9 of error, aris- 

 ing from irregularities in the surface of the 

 mountain. Thus the actual temperature is 

 higher than the calculated temperature un- 

 der depressions of the surface, and lower 

 under peaks ; but for considerable lengths 

 of tunnel the calculated and actual temper- 

 atures substantially agree. Dr. Stapff esti- 

 mated, when the excavations at St. Gothard 

 had been driven to within about one thou- 

 sand yards of the middle of the tunnel, that 

 the temperature at the middle, before pierc- 

 ing the wall between the two excavations, 

 would be 89 for the rock, and the same for 



